According to AAA, the average price of a gallon of unleaded gas in Nebraska as of Monday was $3.83 a gallon, up 28 cents from a week ago.

But some individual markets have gone up even more. In Omaha, for example, Monday’s average price of $3.82 a gallon was 40 cents higher than a week ago. Lincoln actually had one of the smaller week-over-week increases among Nebraska cities, at 19 cents.

Nebraska isn’t the only Midwestern state to see price spikes. Iowa’s average price as of Monday was 38 cents higher than a week ago, while Minnesota’s was up 36 cents and North Dakota’s 30 cents.

The culprit appears to be a refinery outage, according to Patrick De Haan, head of petroleum analysis at GasBuddy.

“Still piecing together exactly what’s gone wrong to cause a huge spike in #gasprices in Group 3 (corn belt states), but it involves more than 1 refinery, bad timing, and issues outside the region exacerbating it,” De Haan said in a Friday post on X (formerly Twitter).

Brian Ortner, a spokesman for AAA Nebraska, said there was some scheduled maintenance at a refinery in Minnesota last week that may have contributed to the quick rise in prices, which he called “uncommon but not unprecedented.”

He also said other factors, such as a rise in the price of oil, also were contributing to the increase.

On Monday, De Haan said that prices should begin to moderate within a day or two and then fall and could be back to where they were before the refinery outage — or even lower — within a week or two.

National prices have stayed pretty much steady, up 2 cents over a week ago but lower than they were a month ago.

De Haan said prices overall should decline in the coming weeks because of a switch to cheaper winter gas blends.

“With most of the nation switching back to cheaper winter gasoline on Saturday, we should see more price decreases for most of the nation in the weeks ahead, barring further refinery disruptions and hurricane season,” he said in a blog post on the Gas Buddy website. “Fall tends to bring falling gas prices, and I’m hoping this year won’t be any different.”